This farm with multi-year and crop rotation has a dynamic response in cost of practice change and nutrient use efficiency. Looking at corn silage production over three years, on average the farm decreased cost per acre as they transitioned to intermediate 4R practices. As the cost decreased on average, the nitrogen use efficiency and nitrogen balance increased over time. This is happening for two reasons. One, the farm is doing an excellent job of crediting the nitrogen that is accumulated in the soil from the alfalfa portion of the rotation into their nitrogen applications. And two, beef manure is applied pre-plant supplying nitrogen to the early growing crop. These are strong practices for building soil health and organic matter.
The nitrogen balance is always negative with the corn silage years and lower in years where there is more first year corn silage. The rotation to alfalfa and the organic nitrogen from the residual beef manure that remains over time helps meet the nitrogen needs of the corn silage crop.
When the crop rotation is corn grain with alfalfa, the accounting for nitrogen from the alfalfa cost did go up as practices shifted to intermediate, but the lower cost in the first year corn is due to the lower fertilizer application from accounting for the nitrogen from the alfalfa crop.